With the ever increasing volume of traffic on roadways, there is a need for more efficient and safer traffic management. The need for local, unidirectional or bi-directional communication, involving specific vehicles and specific information, or between the roadside and vehicles, has been accomplished by various schemes. Some schemes include directional antennas, selected radio frequencies, both continuous and pulsed, and signal encoding. Electronic license plates have also been developed for such local communication. Electronic license plates are license plates that provide both visual information as traditional license plates provide, as well as electronic information and communication. The electronic information can be used for automatic vehicle identification for toll collection purposes or for identification of special vehicles, such as buses to improve scheduling, and police cars and ambulances to improve the efficiency of dispatching such vehicles. Highway vehicles can be electronically monitored by law enforcement agencies. Currently, police use license plates to visually identify vehicles. With electronic license plates, police can use the visual information in conjunction with radio frequency interrogation systems to electronically request and receive the same information provided visually by the license plate, as well as other information, such as the validity of required on-board documents, such as insurance, registration or emission certificates. Other uses of systems using the electronic communication capabilities of electronic license plates include automatic restriction of areas to certain vehicles, traffic control, vehicle theft protection, toll collection, collision avoidance and emergency message communication.
One way to provide electronic information in addition to the visual information is to provide an electronic module in a vehicle for electronically communicating with an interrogator. For example, in U.K. Patent Application GB 2,256,072A to Matsushita Electric Industrial Co. Ltd., a road antenna from an automatic vehicle identification system receives, by radio, data from an identification transponder which is separate from the license plate and is located inside the vehicle. While having an electronic module separate from the license plate accomplishes the goal of providing both electronic and visual information, it is further desirable to have both integrated into a single unit for ease of installation, the ability to use existing structures on vehicles for installation, to optimize antenna location for low power communication between the roadside and the vehicle and to ensure that the visual and electronic information is consistent. Further, it is desirable to have both integrated into a single unit for security reasons. For example, the module containing the electronic information could be stolen from a vehicle and placed inside another vehicle to provide incorrect billing information for a toll collection system.
An example of an integrated electronic license plate wherein both visual and electronic information are provided in a unitary structure is disclosed in U.S. Pat. No. 4,001,822 to Sterzer. The Sterzer electronic license plate has a plurality of layers. The top layer is an electrically non-conductive layer having visual information printed on it where the visual information is similar to the information on a conventional license plate. Behind the top layer are two antenna networks disposed on both sides of a dielectric substrate, a harmonic generator, a signal detector, a connector, internal memory, and an integrated circuit chip to provide the encoder function of the system. This dielectric layer thus serves as a substrate upon which the electronic components of the system are placed and interconnected by printed wire connections. Another non-conducting layer is placed behind the dielectric substrate to provide protection for the antenna network. The antenna networks can receive an interrogation signal from a microwave transmitter and transmit an identification signal in response to the interrogation signal. The Sterzer license plate derives a harmonic signal from the interrogation signal and re-radiates the identification signal at the harmonic frequency. The license plate may further receive external coding from the vehicle.
Integrated electronic license plates are relatively expensive as compared to conventional license plates. Integrated electronic license plates not only include the visual information and structure that conventional license plates have, but also include a number of more costly components, such as the antenna network, the communications electronics and the signal processing electronics. Many states require that license plates be replaced periodically to ensure the integrity of the structure and the quality of the visual information. The expense associated with periodically replacing integrated electronic license plates such as described by Sterzer, however, could be unacceptable.
Integrated electronic license plates integrate all the electronics into a single unit. In many circumstances, however, it is desirable to have both permanent, or restricted, information, such as the license plate number or vehicle identification number, and variable information, such as billing information for toll collection or permit information. The restricted information is preferably stored in a secure location, such that only the issuing authority has access to modify such information while easily accessible electronics would preferably be provided for the variable information such that many organizations could access and utilize them. With integrated electronic license plates, however, the electronics storing such information is not configured in such a manner to allow both secure, permanent information and variable information stored in flexible electronics.
Visual communication of specific motor vehicle identification has long been accomplished by a license plate with a signature of the state and year of registration along with a unique identification number. Police departments and other organizations use the license plate number as identification of a vehicle. Therefore, it is important to such organizations that the license plate number is easily readable. In the past, the surface of the license plate was painted in a bright color for ease of reading the visual information. The optical efficiency of locating and reading license plates has been significantly enhanced by use of an optically retroreflective surface such as 3M brand Scotchlite.TM. Reflective License Plate Sheeting, manufactured by Minnesota Mining and Manufacturing Company of St. Paul, Minn., and printed with the appropriate vehicle designation.
With integrated electronic license plates, however, information associated with a vehicle can be communicated electronically, thereby obviating the need to visually read the license plate number when appropriate electronic readers are present. Moreover, because an electronic license plate can convey more information electronically than a standard license plate can visually, the electronic license plate has many additional uses, such as for obtaining vehicle classifications or permits, for billing purposes in an electronic toll collection system or for a restricted access road system. Because important information is contained in the electronic license plate, it is desirable that the electronic portion of the license plate is secure. More specifically, it is desirable that the portion of the electronics carrying restricted information about a specific vehicle such as the license plate number, expiration date or the vehicle identification number is secure such that they cannot be stolen and switched to another vehicle. It is also desirable, however, that the electronic license plate system provides flexibility in use, such that license plates can be replaced at a relatively low cost and that additional electronic information can be programmed into the system if desired without jeopardizing the integrity of the secured permanent information.
Similar to electronic license plates, electronic road signs have been developed for unidirectional or bi-directional communication between vehicles and the roadside, such as for in-vehicle signing. An electronic road sign has a surface with printed visual information for visual communication of desired information, such as toll collection, traffic control information or dangerous condition warnings. The electronic road sign also has a transmitter to electronically transmit information associated with the road sign. In-vehicle signing allows a vehicle on the roadway to electronically receive the information from the roadside transmitter and display the information inside the vehicle. Also, the information can be communicated by audio within the vehicle. The electronic road sign may also have a receiver to receive information from the vehicle, such as in toll collection to verify transactions, or from traffic management centers to update the message information to be delivered to a vehicle.